1. Field of the Invention
The present invention relates to a high pressure pump.
2. Description of Related Art
In a high pressure pump used for an internal combustion engine, fuel is pressurized in a pressurizing chamber by a plunger, which is reciprocated by rotation of a camshaft, and the pressurized fuel is pumped to fuel injectors. The plunger is reciprocatably supported by a cylinder, which is inserted in a housing of the high pressure pump. JP2008-525713A recites such a high pressure pump. In this high pressure pump, the cylinder, which is configured into a cylindrical tubular form and receives the plunger, is placed in the housing.
However, in the high pressure pump of JP2008-525713A, when the fuel is pressurized in the pressurizing chamber, a pressure of fuel generated in the pressurizing chamber, is applied to the cylinder through the plunger in a direction of removing the cylinder from the housing. Therefore, in order to limit the removal of the cylinder, a counter measure, such as swaging of the housing against the cylinder, needs to be taken.
In the case of the high pressure pump recited in JP2008-525713A, the pressurizing chamber is formed by an end surface of the plunger and an inner wall of the housing. In a case of a high pressure pump recited in WO0047888A1 (corresponding to U.S. Pat. No. 6,631,706B1), a housing contacts and holds a cylinder at a large diameter portion of the cylinder. A pressurizing chamber is formed by an inner wall of the cylinder and a cover member fixed to the housing with screws. In a case of a high pressure pump recited in JP4478431B2, a housing is joined to an upper portion of a cylinder, and a cover is joined between the housing and the cylinder to form a pressurizing chamber.
However, in the case of the high pressure pump recited in JP2008-525713A, a force of a pressure of fuel, which is pressurized in the pressurizing chamber, is applied to the inner wall of the housing, as discussed above. Lately, in order to meet demands of a large flow quantity of fuel and high fuel pressure performance, the pressure of the fuel applied to the inner wall of the housing is very high. Therefore, in order to achieve a sufficient rigidity of the housing against the high fuel pressure, a size of the housing is increased.
Furthermore, in the case of the high pressure pump recited in WO0047888A1 (corresponding to U.S. Pat. No. 6,631,706B1), the pressure of the fuel, which is generated in the pressurizing chamber, is upwardly applied to the cover member, which forms an upper portion of the pressurizing chamber. The cover member is fixed to the housing, so that the upwardly applied force is conducted to the housing. Therefore, in order to achieve a sufficient rigidity of the housing, a size of the housing is increased. Furthermore, in the case of the high pressure pump recited in WO0047888A1 (corresponding to U.S. Pat. No. 6,631,706B1), the large diameter portion of the cylinder contacts the housing, and a cylindrical fuel passage is formed between a small diameter portion of the cylinder and the inner wall of the housing. When rotational motion of a cam of the camshaft is converted into reciprocating motion of the cylinder, the plunger may possibly have precession motion or pendulum motion due to a deviation(s) in a contact position between the cam and a spring seat and/or a contact position between the spring seat and the plunger. The plunger slides in an inside of the small diameter portion of the cylinder. Therefore, when the small diameter portion of the cylinder is not held by the housing, the small diameter portion may possibly be deformed to cause occurrence of seizing of the plunger in the small diameter portion of the cylinder. In order to avoid occurrence of the seizing of the plunger, a wall thickness of the small diameter portion of the cylinder needs to be increased to limit the deformation of the small diameter portion, and thereby a size of the cylinder is increased. In other words, a size of the housing is increased.
Furthermore, in the case of the high pressure pump recited in JP4478431B2, the force, which is exerted by the pressure of the fuel generated in the pressurizing chamber, is applied to a connection between the housing and the cylinder. Therefore, in order to achieve a sufficient rigidity of the housing, a size of the housing is increased, like in the case of JP2008-525713A and the case of WO0047888A1 corresponding to U.S. Pat. No. 6,631,706B1).